1. Field of the Invention
The present invention relates to playback of information from an optical recording medium, and more particularly, to a method and circuit for compensating for time delay between the outputs of a photodetector and detecting a playback signal.
2. Description of the Related Art
In a recording and/or playback apparatus which detects data from an optical recording medium such as a compact disc (CD) or a digital versatile disc (DVD), on which the data is recorded in the form of pits formed on a substrate, by irradiating the pits with light and comparing the amount of reflected light, signals are degraded due to a time delay between the outputs of a photodetector, which is caused by different conditions (width, length, depth, angle, etc) of shapes of data pits, and a time delay which is caused by tangential interference between data.
In conventional detection of a playback signal, as shown in FIG. 1, a pickup unit (P/U) 102 applies a beam emitted from a light source (a laser diode) to a disc 100 to detect information recorded on the disc 100. Then, a multi-division photodetector 104 (also known as a detection sensor), which is usually composed of a photo diode, multi-divides an optical signal reflected from the disc 100 and detects it.
First through fourth current to voltage converters (I/Vs) 106, 108, 110 and 112 respectively convert the multichannel outputs A, B, C and D, which are provided from the photodetector 104 in the form of current signals, into voltage signals. An operational unit 114 sums the voltage signals from the I/Vs 106, 108, 110 and 112 to provide a playback signal RF SUM of a radio frequency (RF).
In a conventional technology which detects a playback signal of data by simply summing the outputs of the I/Vs 106, 108, 110 and 112, the playback signal may be distorted or degraded during operation due to time delay between the outputs of the I/Vs 106, 108, 110 and 112, which is caused by different shape conditions of data pits formed on a disc and interference between data.
Meanwhile, for optical discs, a large recording capacity and high speed playback is desired for recording and/or playback of high definition (HD) images. Moreover, as the characteristics of systems move toward high density and high multiple-speed, distortion and degradation of playback signals become more serious, and thus a great deal of labor and additional cost are incurred when implementing systems. The time delay between the outputs of a photodetector causes distortion of a playback signal. When the amplitude of a playback signal is not normally detected, the performance of a system is decreased.